1. Field of Invention
The present invention relates to an apparatus and an adjusting technology for a uniform thermal processing and particularly for uniformly heating wafers.
2. Description of the Related Art
Along with the advances of science and technology and the steady enhancement of living quality plus the continuously growing of computers and the peripheral industries thereof, the IC (integrated circuit) application fields are wider and wider. As to the IC devices in current applications, the silicon wafers are used as the base material for the most IC substrates. On a wafer, a number of semiconductor processes, such as layer deposition, lithographing, etching, removing the photoresist, and followed by packaging and testing, etc. are performed to accomplish the IC device fabrication.
In the above-mentioned semiconductor processes, especially in thermal annealing and thermal oxidizing processes, “temperature” is one of the most important production parameters. A lately developed “rapid thermal processing” (RTP) provides an effective and efficient thermal processing for the wafers. In this thermal processing technology, however, one of the critical issues is how to reach a uniform temperature distribution within a wafer as well as from wafer to wafer.
FIG. 1A is a simplified cross-sectional view, schematically showing a conventional thermal processing apparatus. FIG. 1B is a plan view, schematically showing a set of heating lamps in FIG. 1A. Referring to FIG. 1A and FIG. 1B, a conventional thermal processing apparatus 100 mainly comprises a chamber 110, a supporter 120 and a set of heating lamps 130. Wherein, the supporter 120 and the set of heating lamps 130 are disposed inside the chamber 110 and are separated by a thermally transparent plate 140, such as a quartz plate. The set of heating lamps 130 locates above the supporter 120 and comprises a plurality of heating lamps 132 and reflectors 134. A wafer 10 is placed on the supporter 120. The set of heating lamps 130 is used for heating the wafer 10.
Prior to heating the wafer 10, an individual heating lamp 132 and the appropriate reflector 134 thereof must be adjusted to get a certain heat flux distribution on the wafer 10 to meet the requirements of the conventional thermal processing process. In general, by controlling the distance between the heating lamp 132 and the wafer 10, the shape of the reflector 134 and the heating power applied to the heating lamp 132, a desired contribution by an individual heating lamp 132 on the overall heat flux distribution of the wafer 10 will be obtained. In this way, the individual heating lamp adjustment is completed.
Next, according to the heat flux distribution on the wafer 10 by an individual heating lamp 132, the overall heat flux distribution on the wafer 10 by a set of heating lamps 130 is thus estimated. Since the wafer 10 is in a disk shape, these heating lamps 132 are arranged in an axi-symmetric array to form a set of heating lamps 130 as shown in FIG. 1B. Remarkably, the local area of the wafer 10 right under the heating lamp 132 receives a local maximum heat flux due to the relatively shortest distance between the heat source and the heated spot. On the other hand, the area of the wafer 10 farther away from the heating lamp 132 therefore receives a lower heat flux. Accordingly, it is very hard to meet a uniform requirement of the heat flux distribution on the wafer 10.
To make the heat flux distribution on the wafer 10 uniform, a rotatable design of a supporter 120 with a proper velocity was developed. Thus, the heat flux distribution on wafer 10 along a circumferential direction is relatively uniform. FIG. 2 illustrates the heat flux distribution on a wafer with the rotating supporter in a conventional thermal processing apparatus. In FIG. 2, the chart of heat flux distribution on the wafer 10, the abscissa represents radial positions on the wafer 10 (in unit of cm), the ordinate represents the heat fluxes received on the wafer 10 (in unit of W/cm2), and the zero value of abscissa represents the center of the wafer 10.
Referring to FIG. 1B and FIG. 2, the local area, on the upper surface of wafer 10 and between two adjacent rings of heating lamps 132, is a non-perpendicular incidence zone and the heat flux thereon is relatively lower. Even if the wafer 10 rotates, the accumulated heat density on this non-perpendicular incidence zone is still lower than that on the zone right under the heating lamp 132. The wafer 10 with a proper rotating velocity may get a relatively uniform heat flux distribution along a circumferential direction (P-direction shown in FIG. 1B). Along the radial direction of the wafer 10 (R-direction shown in FIG. 1B), however, the heat flux distribution thereon still has a big fluctuation. As shown in FIG. 2, the fluctuating amplitude is about ±5%. The so-called “fluctuating amplitude” herein means (peak value−average value)/average value.
Thus, excessive fluctuating amplitude of heat flux distribution on a wafer will produce a thermal stress. It may cause dislocation and crossover, i.e. bare wire connection in the IC. In addition, it may also cause a discrepant chemical-reaction rate on the wafer or from wafer to wafer. All those will reduce the production yield of wafers in company with an increased production cost. Along with the tendency of larger-size wafer and tinier-size IC, the problems due to excessive temperature non-uniformity in a wafer would become more serious and worse.